In recent years, an optical switch module, using a light deflecting element having an electro-optical effect, has been proposed (for example, refer to the U.S. Pat. No. 6,504,966).
Such an optical switch module has the following structure. As shown in, for example, FIGS. 1A and 1B, in the optical switch module, light deflecting elements 101 and 102, formed of electro-optical materials (for example, electro-optical crystals, such as PZT or PLZT), are mounted onto a slab optical waveguide substrate unit 100.
That is, as shown in, for example, FIGS. 1A and 1B, the slab optical waveguide substrate unit 100 has integrally formed, input channel optical waveguides (input channel optical waveguide array) 103 to which a light signal is input, collimator lenses (input-side lens array) 104 that convert the input light signal into parallel light (collimated light), a slab optical waveguide 105 that allows the light signal converted into the parallel light to propagate therethrough, light-converging lenses (output-side lens array) 106 that converge the light signal (propagating parallel light), and output channel optical waveguides (output channel optical waveguide array) 107 to which the light signal is output. A first light-deflecting element mounting opening 112, to which the light deflecting elements 101 are mounted, and a second light-deflecting element mounting opening 113, to which the light deflecting elements 102 are mounted, are formed in the slab optical waveguide array substrate unit 100. In FIG. 1B, reference numeral 111 denotes a core layer, reference numeral 114 denotes a lower clad layer, and reference numeral 115 denotes an upper clad layer.
The input-side light deflecting elements (first light-deflecting element array) 101 and the output-side light deflecting elements (second light-deflecting element array) 102 are formed by forming thin-film slab optical waveguides 109, formed of electro-optical materials (for example, electro-optical crystals, such as PZT or PLZT), onto respective conductive substrate units 108; by forming prism electrodes 110 on a surface of each slab optical waveguide 109; and by polishing end surfaces.
In the optical switch module, the input-side light deflecting elements 101 are mounted to the first light-deflecting element mounting opening 112 disposed between the collimator lenses 104 and the slab optical waveguide 105 at the slab optical waveguide substrate unit 100. The output-side light deflecting elements 102 are mounted to the second light-deflecting element mounting opening 113 disposed between the slab optical waveguide 105 and the light-converging lenses 106.
In the optical switch module having such a structure, application of a predetermined voltage to the prism electrodes 110 (formed at the input-side light deflecting elements 101 and the output-side light deflecting elements 102) results in the following. For example, as shown in FIG. 1A, light signals, input from the input channel optical waveguides 103 and converted into parallel lights by the collimator lenses 104, are deflected by the input-side light deflecting elements 101, propagate through the slab optical waveguide 105, are deflected again by the output-side light deflecting elements 102, are converged by the light-converging lenses 106, and are focused at the predetermined output channel optical waveguides 107. This causes a path of the light signal that is input from the input channel optical waveguide 103 to be switched, so that the light signal is output from the predetermined output channel optical waveguide 107.
An example of a method of manufacturing the optical switch module having the above-described structure is given below. First, as shown in, for example, FIG. 2A, a slab optical waveguide substrate unit 100 is formed so that input channel optical waveguides 103, an input-side lens array 104, a first light-deflecting element mounting opening 112, a slab optical waveguide 105, a second light-deflecting element mounting opening 113, an output-side lens array 106, and an output channel optical waveguide 107 are integrally formed. Next, as shown in, for example, FIGS. 2B and 2C, a first light-deflecting element array 101 and a second light-deflecting element array 102 are mounted to the light-deflecting element mounting opening 112 and to the light-deflecting element mounting opening 113 in a slab optical waveguide substrate unit 100, respectively. (For example, refer to the U.S. Pat. No. 6,504,966).
In this manufacturing method, since the number of joints that are joined with an adhesive is small, it is possible to restrict the influence resulting from positional displacement with time at the joints. For mounting the light deflecting element arrays 101 and 102 onto the slab optical waveguide substrate unit 100, active alignment is performed while monitoring the intensity of output light. During the active alignment, when light (monitor light, propagating light) that propagates through the slab optical waveguide is displaced from a predetermined traveling angle, the propagating light does not combine at the output channel optical waveguides 107, and positional adjustment of the output-side lens array (light-converging lens array) 106 cannot be carried out either. Therefore, it is difficult to perform the alignment (active alignment) of the first light-deflecting element array 101 and the second light-deflecting element array 102.
The causes of the angular displacement of the propagating light are, for example, polishing precision of the light deflecting elements and crystal characteristics (ununiformity in film thicknesses and refractive indices) of the light deflecting elements.
Another example of manufacturing the optical switch module is given below. For example, as shown in FIGS. 3A to 3D, each component making up the optical switch module is individually formed. The components are located where an input channel optical waveguide array 103 and an input-side lens array 104 are formed, the component where a first light-deflecting element array 101 is mounted, the component where a slab optical waveguide 105 is formed, the component where a second light-deflecting element array 102 is mounted, and the component where an output-side lens array 106 and an output channel optical waveguide array 107 are formed. These components are joined to each other with a butt-joint, so that the optical switch module is manufactured. (For example, refer to the U.S. Pat. No. 6,504,966).
In this manufacturing method, it is possible to join each component as a result of active alignment while monitoring the intensity of output light. However, the characteristics of the optical switch module may become deteriorated due to positional displacement with time at each joint. In particular, if the number of such joints is large, the characteristics of the optical switch module tend to be deteriorated due to positional displacement with time at each joint.
Accordingly, the related art has the problem that alignment by active alignment cannot be reliably performed due to an angular displacement of propagating light.